Method of manufacturing mercury commutation switch



A. S. BACKUS Jan. 24, 1961 METHOD OF MANUFACTURING MERCURY COMMUTATION SWITCH Filed Aug. 7, 1958 I 1 Iv I a O NVENTOR ED 5. BACKUS MMM 54M ATTORNEYS.

METHOD OF MANUFACTURING MERCURY COMMUTATIQIN SWITCH Alfred S. Backus, Passaic, N.'.l., assig'nor to Mycaiex Corporation of America, Clifton, N..l., a corporatien of New York Filed Aug. 7, 1958, Ser. No. 753,682

3 Claims. (Cl. 29-15555) This invention relates to an improved method of manufacturing a mercury commutation switch.

This application is a continuation in part of my earlier filed propending application, Serial No. 665,077, filed by me June 11, 1957 for Method of Manufacturing Mercury Commutation Switch.

The art of commutation has gone through a great transformation as a result of extreme requirements of the field of telemetry. In the telemetry field commutators are employed to selectively close a plurality of circuits each of which transmits information of a specific nature. Accordingly, the information in each of the circuits may be transmitted sequentially over one channel of communciation rather than be transmitted simultaneously over a plurality of channels of communication. Thus by the inclusion of a commutator the telemetering apparatus can be greatly simplified.

The electrical pulses which are equivalent to information in the plurality of circuits mentioned above, are usually of relatively small magnitude. One of the great problems in telemetry commutation has been to switch from circuit to circuit without introducing such a high level of switching noise as to obscure the signal repre senting the information to be transmitted. One form of commutator which has been successfully used in telemetry and which meets this rigorous condition of low switching noise has been the type normally called mercury commutators. In such commutators a channel is provided for a ball of mercury and a plurality of contacts extend into the channel. In addition, a continuous electrical member is in communication with the channel. As the ball of mercury moves through the channel, it sequentially closes circuits extending from each contact to the continuous conducting member whereby to sequentially close each of a plurality of electrical circuits.

Considerable difficulty has been encountered in fabricating mercury switches of the type described. It is therefore the major object of the present invention to provide a new and improved method for making mercury commutation switches.

A further object of the present invention is the provision of a new and improved method for manufacturing mercury commutation switches including vitrco-micaceous insulating material therein.

The above and other objects, characteristics and features of the present invention will be more fully understood from the following description taken in connection with the accompanying illustrative drawing.

in the drawing:

Fig. 1 is a transverse sectional view of a mercury commutation switch embodying the present invention; and

Fig. 2 is a rear plan view of the switch shown in Fig. 1.

Referring now to the drawing in detail, the mercury commutation switch is generally designated by the reference numeral 10. The switch comprises an electrically continuous metallic element 12 which is spaced from a plurality of contacts 14 by suitable insulating material SllfitCS Patent 2,968,861 Patented Jan. 24, 1961 2. 16 and 18. Preferably, the metallic member 12 and the contacts 14 are made of stainless steel and the insulating materials. designated as 16 and 18 are vitreomicaceous materials such as glass-bonded mica and ceramoplastic. The materials named are preferred because the stainless steel and. the vitreo-micaceous material have coefiicients of thermal expansion which are extremely close. Accordingly, there is little or no tendency of the materials to part due to changes in temperature. Furthermore, the stainless steel material is preferred due to its extreme ruggedness, good electrical conductivity and ease of fabrication. The vitreo-micaceous material is extremely desirable not only due to its matching thermal coefficient, but further due to its dimensional stability, its high dielectricstrength, its superior resistance to high temperatures, and its excellent mechanical properties.

Essentially the metallic member 12 is a disc havinga central hub 20, a part of which is adapted to be connected to a suitable drive shaft 22. The remainder of the disc is substantially planar having a front surface 24 and a rear surface 26 connected by a peripheral side wall 28. The front surface 24 of member 12 is provided with an annular groove 30, the purpose of which will become more apparent hereinafter. The rear surface'26 is provided with an annular groove 31 having a relatively wide annular groove portion 32 which is in communication with a narrower annular groove portion 34. The contacts 14 extend through groove portion 32 and into groove portion 34. It is groove portion 34 which defines the annular channel for a ball of mercury herein designated by the reference numeral 36. In order to hold the contacts 14 with their tips in the channel 34, ring 16 of vitreo-micaceous material and preferably ceramoplastic is molded into annular groove portion 32. It will be noted that there is no recentrant portion or other mechanical means to hold the ceramoplastic ring 16 in position in the groove portion 32. In order to effect this holding and to efiect it so that there will be no movement of the ring 16 relative to member 12, cerarnoplastic material 18 is formed around a portion of the front surface 24 of metallic member 12, the peripheral side wall 28 thereof, and the rear wall 26 thereof. By so doing, the vitreomicaceous material 18 encloses the ceramoplastic ring 16 and thereby holds it in groove portion 32. Although the insulating material 18 is molded around metallic member 12 in such a manner that there is no room for movement of the material 18 relative to the member 12, the vitreomicaceous material 18 fills the annular groove 30 in surface 24 of member 12 whereby to firmly lock the vitreomicaceous material 18 relative to the metallic member 12. Preferably, the vitreo-micaceous material 18 is a ceramoplastic although glass-bonded mica or other moldable insulation will be satisfactory.

The ceramoplastic ring 16 and the annular groove 34 form between them the annular channel 34 in which is positioned a ball of mercury 36. As is well known, mercury is an excellent electrical conductor. Moreover, if a potential exists between a contact 14 and metallic member 12 and mercury ball 36 comes into contact with both the contact 14 and the metallic member 12, it closes an electrical circuit. By providing any suitable means which forms no part of the present invention, mercury ball 36 can be made to rotate about annular channel 34 and thereby sequentially close electrical circuits between each of the contact 14 and the metallic member 12. Suitable electrical conductors can be connected to the contacts 14 and the member 12 in order to supply electrical energy to or receive electrical pulses from these members.

In accordance with the present invention, the mercury commutation switch hereinbefore described is fabricated first by machining a stainless steel member into the form of the disc 12 hereinbefore described.

The second step in making the commutator plate is to mold the insulating ring 16 together with the contacts 14. This may be done in a mold having a mold cavity of annular configuration and further having provision for receiving inserts such as the contacts 14. This provision for inserts is generally a plurality of holes or cavities adapted to receive the contacts 14 with close tolerance. The contacts are first disposed in the mold as stated above and the mold is sprayed with a suitable parting agent such as oil. The mold is preferably heated to a temperature 500 F. and 650 F., preferably 600 F. The mold is closed and vitreo-micaceous material such as ceramoplastic which has been preheated to between about 1150 F. and 1350" F. (preferably 1300 F.) to render it plastic is then forced into the annular mold cavity by a ram at pressures between 30,000 psi. and 50,000 p.s.i. (preferably 40,000 p.s.i.). After the material is forced into the mold cavity the pressure is held for sufficient time to allow the vitreo-micaceous material to harden and then the finished product is ejected from the mold. The finished product, of course, will consist of a circular row of spaced contacts 14 which are imbedded in an annular ring of ceramoplastic material. The ring 16 is proportioned to be inserted in annular groove portion 32 with close tolerances whereby the ring 16 and the groove portion 34- in the metal member 12 define between them the annular cavity 34.

It will be clear that the ring 16 is at best pressedfitted into the groove portion 32 and such a fit will not suffice to hold the ceramoplastic ring 16 and contacts 14 fixed relative to member 12. Accordingly, a second molding step is performed wherein the assembled metallic member 12 and ceramoplastic ring 16 and contacts 14 together form an insert in a mold cavity which is adapted to receive the vitreo-micaceous material 18. The vitreomicaceous material 18 is also preferably ceramoplastic and the temperatures and pressures presented above with respect to the molding of ring 16 are satisfactory for molding the envelope 18. After the ceramoplastic material forming envelope 18 sets, the plate may be ejected from the second mold cavity and is substantially in the form shown in Figs. 1 and 2. Thereafter, a small hole is drilled through ceramoplastic layers 18 and 16 to permit the introduction of mercury 36 into the channel 34. After this material is introduced the hole may be closed as by a suitable epoxy resin or other suitable sealing means. In the alternative, one of the contacts 14 can be formed in the shape of a hollow tube and this contact may be used as a channel for introducing the mercury into annular channel 34. After the mercury is introduced, the hollow contact 14 may be closed as by solder.

The two-step molding operation described above greatly simplifies the fabrication of mercury switches and greatly reduces their cost. Moreover, by using injection or precision molding techniques, there is little or no finishing required after the molding operations are completed. Furthermore, and as has been stated hereinbefore, by utilizing ceramoplastic material a switch of great dimensional stability and high thermal endurance is provided.

While I have herein shown and described the preferred form of the present invention, various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of this invention.

Having now described my invention, what I claim as new and desire to secure by Letters Patent is:

1. The method of manufacturing a mercury commutator, comprising the steps of forming a relatively wide annular groove on a flat surface of a stainless steel plate having two flat surfaces and a peripheral side Wall, forming on the inner surface of said relatively wide groove a relatively narrow annular groove, molding an insulating ring of vitreo-micaceous material and having -a plurality of equi-spaced contacts with a predetermined spacing therebetween distributed in a circular row with the ends of said contacts extending through said insulating ring so that the ends of said contacts will be exposed beyond opposed surfaces of said insulating ring, said ring being adapted to fill said wide annular groove and said contacts being adapted to extend into said narrow annular groove, disposing said insulating ring in said wide annular groove with said contacts extending into said narrow annular groove, molding vitreo-micaceous material around portions of said flat surfaces and around said peripheral side wall and in surface-to-surface relation with the vitreo-micaceous ring in said wide groove so that the ends of said contacts remain exposed and to secure said insulating ring therein, whereby said insulating ring partially defines an annular channel which is further defined by the portions of said stainless steel plate surrounding said narrow groove, and then introducing and confining a quantity of mercury in said annular channel to have electrical continuity only between said stainless steel plate and said spaced contacts sequentially during movement of said mercury.

2. The method of manufacturing a mercury commutator, comprising the steps of forming a relatively wide annular groove on a fiat surface of a stainless steel plate having two fiat surfaces and a peripheral side wall, forming on the inner surface of said relatively wide groove a relatively narrow annular groove, molding an insulating ring of ceramoplastic material and having a plurality of equi-spaced contacts with a predetermined spacing therebetween distributed in a circular row with said contacts extending through said insulating ring and the ends thereof being exposed beyond opposed surfaces of said insulating ring, said ring being adapted to fill said wide annular groove and said contacts being adapted to extend into said narrow annular groove, disposing said insulating ring in said wide annular groove with said contacts extending into said narrow annular groove, then molding ceramoplastic material around portions of said flat surfaces and around said peripheral side wall and in surface-to-surface relation with said ceramoplastic ring in said wide groove so that the exposed ends of said contacts remain exposed and to secure said ceramoplastic ring therein, whereby said ceramoplastic ring partially defines an annular channel which is further defined by the portions of said stainless steel plate surrounding said narrow groove, and drilling a hole through both said ceramoplastic ring and said surrounding ceramoplastic into said annular channel, introducing through said hole a sufiicient amount of mercury to bridge the distance between said contacts and said stainless steel plate but insufficient to bridge the spacing between adjacent contacts during movement of said mercury, and then sealing said hole.

3. The method of manufacturing a mercury commutator, comprising the steps of forming a relatively wide annular groove on a flat surface of a stainless steel plate having two flat surfaces and a peripheral side wall, forming on the inner surface of said relatively wide groove a relatively narrow annular groove, molding an insulating ring of ceramoplastic material and having a plurality of equi-spaced tubular contacts with a predetermined spacing therebetween distributed in a circular row with said contacts extending through said insulating ring so that the ends of said contacts are exposed beyond opposed surfaces of said insulating ring, said ring being adapted to fill said wide annular groove and said contacts being adapted to extend into said narrow annular groove, disposing said insulating ring in said wide annular groove with said contacts extending into said narrow annular groove, then molding ceramoplastic material around portions of said flat surfaces and around said peripheral side wall and in surface-to-surface relation with the molded ceramoplastic material in said wide groove so that the exposed ends of said contacts remain exposed and to secure said ceramoplastic material therein, whereby said ceramoplastic material partially defines an annular channel which is further defined by the portions of said stainless steel plate surrounding said narrow groove, in- 5 troducing through one of said tubular contacts a sufficient amount of mercury to bridge the distance between said contacts and said stainless steel plate but insuffioient to bridge the spacing between adjacent contacts during rotational movement of said stainless steel plate, and 10 then sealing the passages in said tubular contacts.

References Cited in the file of this patent UNITED STATES PATENTS Brennan July 21,

Ionard et a1. Jan. 10,

Squier Feb. 27,

Carey Mar. 11,

FOREIGN PATENTS Great Britain June 9, 

